DNA Replication LO Flashcards
what does semi-conservative mean?
Newly replicated DNA has one parental strand and one daughter strand
what does bidirectional mean?
replication begins at a site of origin and simultaneously moves out in both directions from this point
how many sites of origin do prokaryotes have?
1
how many sites of origin do eukaryotes have?
multiple
What is a replication fork?
site at which DNA synthesis is occurring
what do origin binding proteins do?
recognize and bind onto origins of replication
what types of nucleotides are origins of replication rich in?
A and T
what do helicases do?
unwinds DNA ahead of the replication fork by breaking hydrogen bonds between strands
what do single-strand binding proteins do?
bind to each single strand of DNA and hold it in single stranded conformation
What do topoisomerases do?
prevent extreme supercoiling of parental helix that would result as a consequence of unwinding at replication fork
how do topoisomerases prevent supercoiling?
break and rejoin DNA strands
what is important about DNA gyrase in prokaryotes?
can be inhibited by quinolones in treatment of disease
which direction does DNA synthesis proceed?
5’ - 3’
how does DNA polymerase work?
adds deoxyribonucleotides to the 3’ hydroxyls of RNA primers and subsequently to ends of growing DNA strands
what does a primase do?
catalyzes the addition of RNA primer to begin replication
what are the 2 types of DNA polymerases in prokaryotes?
DNA pol I and DNA pol III
what is the major replicative enzyme for DNA and why?
DNA pol III because it has a sliding clamp that keeps it attached to the DNA template
what does DNA pol I do?
mediates replacement of RNA primers with DNA
through which 3 processes does DNA pol I work?
a. 5’ - 3’ exonuclease activity for RNA primer removal
b. 3’ - 5’ exonuclease activity for proofreading
c. 5’ - 3’ DNA polymerase activity
what is the function of DNA Pol III
it is the major replicative enzyme in DNA synthesis
why is DNA pol III the major replicative enzyme?
because it has a sliding clamp which keeps it attached to the DNA over a long distance
what are the 3 DNA polymerases in eukaryotes?
Pol α Pol δ and Pol ε
what is the function of DNA pol α?
synthesizes the first 20 DNA nucleotides after the RNA primer
what types of activity are located in DNA pol α? (2)
primase activity and DNA polymerase activity
NO PROOF READING
which polymerase performs lagging strand synthesis in eukaryotes?
Pol δ
which polymerase performs leading strand synthesis?
Pol ε
what serves as the primer for DNA polymerase in cells?
RNA
what enzyme places the RNA primer?
primase
what is the classification of primase?
DNA-dependent RNA polymerase
in relation to the replication fork, which direction does the leading strand replicate?
towards the replication fork
in relation to the replication fork, which direction does the lagging strand replicate?
away from the replication fork
what is the name for the short sequences of DNA located on the lagging strand of DNA replication?
okazaki fragments
are okazaki fragments longer in eukaryotes or prokaryotes?
prokaryotes (1000-2000 bp)
eurakryotes (100-200 bp)
how are RNA primers removed?
through 5’-3’ exonuclease
DNA pol I in E. coli
what does DNA Pol I require on the DNA strand to start DNA synthesis?
3’ -OH primer (RNA)
which enzyme joins okazaki fragments together?
DNA ligase
DNA ligase joins which 2 groups together?
3’ hydroxyl group with 5’ phosphate group of 2 polynucleotide chains
Why is fidelity of replication so high?
- hydrogen bonds between bp
- geometry of AT and CG in active site of polymerase
- proofreading through 3’-5’ exonuclease activity
- post-replication repair process
what is reverse transcription and what enzyme performs this process?
synthesis of RNA to DNA
reverse transcriptase
what is reverse transcriptase categorized as?
RNA dependent DNA polymerase
what is the genetic material in retroviruses?
RNA
what enzyme in eukaryotic cells has reverse transcriptase activity?
telomerase
what is the job of telomerase?
to restore the ends of chromosomes (telomeres) in human cancer and stem cells
how does telomerase work?
uses RNA template and reverse transcriptase activity to restore telomeres
what is the “end replication problem”?
leading strand can be synthesized to the very end but lagging strand cannot. This causes shortening of telomeres in cells
what happens when telomeres become too short after many round of replication?
cell death
in what types of cells is telomerase activity repressed?
normal somatic cells
why is telomerase a potential target in anti-cancer drugs?
because telomerase is not repressed in cancer cells, telomeres continue to be restored and thus cell death never occurs
